1. Field of the Invention
The present invention provides a method of and materials for depositing thin highly conducting lines on large area insulating substrates.
2. Prior Art
The printed circuit art is replete with methods of obtaining conducting lines on insulating substrates. Attempts to obtain high density circuitry have used any of a number techniques from vacuum deposition to voltaically depositing metals. Another art requiring thin conducting lines in high density over large areas is the gas panel technology. Commonly used techniques are either those used in the printed circuit technology or screening techniques.
None of the foregoing references relate to processes directed to depositing a metal on a substrate employing photochemical steps in order to produce conductive lines for the selective electrodeposition of a metal. Moreover, none of the references which we have developed teaches the use in depositing a metal on a substrate of .pi.-donor compounds similar to those which are the subject of the present invention.
The Tamai et al patent (U.S. Pat. No. 3,565,613) relates to a reproduction process in which a photoconductive layer consisting of zinc oxide powders uniformly depersed in an insulating resin is image-wise exposed to form latent images. The latent images consist of the electroconductive difference between the exposed and unexposed areas. After exposure, the latent images are subjected to electrolysis in an electrolyte bath containing a material capable of forming visible images by an oxidation or reduction process, and does not involve the deposition of a metal on the substrate. The materials contemplated for reaction with the latent image are dyes capable of undergoing oxidation reduction type reactions. In contrast, the deposition of .pi.-donor salts produces electrical conductivity in the exposed areas of the substrate.
The Reithel patent (U.S. Pat. No. 3,220,939) also relates to an electrolytic reproduction process described as in the Tamai patent.
Haberecht (U.S. Pat. No. 3,436,468) relates to a method of depositing a metal on a substrate. In accordance with the teachings of Haberecht, the substrate is coated with a polymer which is subsequently exposed to an electron beam. The electron beam decomposes the polymer to alter its chemical structure in selected paths. When the substrate is contacted with an electrolytic solution, the metal deposits onto the path of decomposed polymers that have been exposed to the electron beam. The patent does not clearly indicate the bases for the deposition, however, it appears that the path of decomposed polymer exhibits a lower resistance during electrodeposition.
Ferrara (U.S. Pat. No. 3,791,340) discloses a method of depositing a metal pattern on a surface of a substrate. The surface of the substrate is sensitized with a photosensitive palladium sensitizer or catalyst. The sensitized surface is exposed to ultraviolet radiation to delineate an unexposed pattern corresponding to the desired metal pattern. The palladium sensitizer in its initial state is capable of participating in electrodeposition, but upon exposure, the palladium sensitizer is rendered incapable of such participation. Upon immersing the exposed surface in a suitable electroless metal deposition solution, deposition occurs only in the areas of the unexposed palladium sensitizer.
Lee (U.S. Pat. No. 3,748,109) relates to a process for producing printed circuits, wherein a metal phosphorus compound is selectively formed on a substrate, using a photomask. The metal phosphorus compound is in the low oxidation state so that the substrate can be subjected to electroless or electrolytic treatment in order to deposit metal at the location of the metal phosphorus compound.
A method for optically printing conductive characters using organic .pi.-electron donor compounds is disclosed in copending Application Ser. No. 591,992 to Edward M. Engler, Frank Kaufman and Bruce A. Scott and assigned to the same assignee as the present invention.
It is disclosed therein the organic "charge transfer" compounds which are low ionization potential donors and their charge transfer salts formed by oxidation with organic acceptors, when deposited from an halogenated hydrocarbon solvent and radiated with active radiation provided highly conducting images. Examples of organic .pi.-electron donor compounds disclosed therein includes tetrathiafulvalene (TTF) tetraselenafulvalene (TSeF); Dithiadiselenafulvalene (DTDSeF), hexamethylene-tetrathiafulvalene, tetramethylene tetrathiafulvalene (TMTTF), tetrathiatetracene and the like. Generally the method dislosed in the aforementioned application included the steps of depositing the organic .pi.-electron donor compound upon a substrate from a halogenated hydrocarbon (halocarbon) solution thereof. The deposited compound is then irradiated by actinic radiation in a predetermined pattern to give a colored, highly conductive image. It should be understood that the method of Application of Ser. No. 591,992 is incorporated herein by reference.